Assessing Interaction in Case-Control Studies

Physical Activity Modifies the Risk of Incident Cardiac Conduction Disorders Upon Inflammation: A Population-Based Cohort Study

BACKGROUND

Emerging evidence suggests a central role for inflammation in cardiac conduction disorder (CCD). It is unknown whether habitual physical activity could modulate the inflammation-associated risks of incident CCD in the general population.

METHODS AND RESULTS

This population-based cohort was derived from the China Kailuan study, including a total of 97 192 participants without prior CCD. The end points included incident CCD and its subcategories (atrioventricular block and bundle-branch block). Systemic inflammation was indicated by the monocyte-to-lymphocyte ratio (MLR). Over a median 10.91-year follow-up, 3747 cases of CCD occurred, with 1062 cases of atrioventricular block and 2697 cases of bundle-branch block. An overall linear dose-dependent relationship was observed between MLR and each study end point (all P-nonlinearity≥0.05). Both higher MLR and physical inactivity were significantly associated with higher risks of conduction block. The MLR-associated risks of developing study end points were higher in the physically inactive individuals than in those being physically active, with significant interactions between MLR levels and physical activity for developing CCD (P-interaction=0.07) and bundle-branch block (P-interaction<0.05) found. Compared with those in MLR quartile 2 and being physically active, those in the highest MLR quartile and being physically inactive had significantly higher risks for all study end points (1.42 [95% CI, 1.24-1.63], 1.62 [95% CI, 1.25-2.10], and 1.33 [95% CI, 1.13-1.56], respectively, for incident CCD, atrioventricular block, and bundle-branch block).

CONCLUSIONS

MLR should be a biomarker for the risk assessment of incident CCD. Adherence to habitual physical activity is favorable for reducing the MLR-associated risks of CCD.

Time to Surgical Treatment and Facility Characteristics as Potential Drivers of Racial Disparities in Breast Cancer Mortality

BACKGROUND

Black women are more likely to die of breast cancer than White women. This study evaluated the contribution of time to primary surgical management and surgical facility characteristics to racial disparities in breast cancer mortality among both Black and White women.

METHODS

The study identified 2224 Black and 3787 White women with a diagnosis with stages I to III breast cancer (2010-2014). Outcomes included time to surgical treatment (> 30 days from diagnosis) and breast cancer mortality. Odds ratios (ORs) and 95% confidence intervals (CIs) associating surgical facility characteristics with surgical delay were computed, and Cox proportional hazards regression was used to compute hazard ratios (HRs) and 95% CIs associating delay and facility characteristics with breast cancer mortality.

RESULTS

Black women were two times more likely to have a surgical delay (OR, 2.15; 95% CI, 1.92-2.41) than White women. Racial disparity in surgical delay was least pronounced among women treated at a non-profit facility (OR, 1.95; 95% CI, 1.70-2.25). The estimated mortality rate for Black women was two times that for White women (HR, 2.00; 95% CI, 1.83-2.46). Racial disparities in breast cancer mortality were least pronounced among women who experienced no surgical delay (HR, 1.81; 95% CI, 1.28-2.56), received surgery at a government facility (HR, 1.31; 95% CI, 0.76-2.27), or underwent treatment at a Commission on Cancer-accredited facility (HR, 1.82; 95% CI, 1.38-2.40).

CONCLUSIONS

Black women were more likely to experience a surgical delay and breast cancer death. Persistent racial disparities in breast cancer mortality were observed across facility characteristics except for government facilities.

Exploring interaction effects in small samples increases rates of false-positive and false-negative findings: results from a systematic review and simulation study

OBJECTIVE

To give a comprehensive comparison of the performance of commonly applied interaction tests.

METHODS

A literature review and simulation study was performed evaluating interaction tests on the odds ratio (OR) or the risk difference (RD) scales: Cochran Q (Q), Breslow-Day (BD), Tarone, unconditional score, likelihood ratio (LR), Wald, and relative excess risk due to interaction (RERI)-based tests.

RESULTS

Review results agreed with results from our simulation study, which showed that on the OR scale, in small sample sizes (eg, number of subjects ≤ 250) the type 1 error rates of the LR test was 0.10; the BD and Tarone tests showed results around 0.05. On the RD scale, the LR and RERI tests had error rates around 0.05. On both scales, tests did not differ regarding power. When exposure prevented the outcome RERI-based tests were relatively underpowered (eg, N = 100; RERI power = 5% vs. Wald power = 18%). With increasing sample size, difference decreased.

CONCLUSION

In small samples, interaction tests differed. On the OR scale, the Tarone and BD tests are recommended. On the RD scale, the LR and RERI-based tests performed best. However, RERI-based tests are underpowered compared with other tests, when exposure prevents the outcome, and sample size is limited.

Contribution of 20 single nucleotide polymorphisms of 13 genes to dyslipidemia associated with antiretroviral therapy

BACKGROUND

HIV-1 infected individuals have an increased cardiovascular risk which is partially mediated by dyslipidemia. Single nucleotide polymorphisms in multiple genes involved in lipid transport and metabolism are presumed to modulate the risk of dyslipidemia in response to antiretroviral therapy.

METHODS

The contribution to dyslipidemia of 20 selected single nucleotide polymorphisms of 13 genes reported in the literature to be associated with plasma lipid levels (ABCA1, ADRB2, APOA5, APOC3, APOE, CETP, LIPC, LIPG, LPL, MDR1, MTP, SCARB1, and TNF) was assessed by longitudinally modeling more than 4400 plasma lipid determinations in 438 antiretroviral therapy-treated participants during a median period of 4.8 years. An exploratory genetic score was tested that takes into account the cumulative contribution of multiple gene variants to plasma lipids.

RESULTS

Variants of ABCA1, APOA5, APOC3, APOE, and CETP contributed to plasma triglyceride levels, particularly in the setting of ritonavir-containing antiretroviral therapy. Variants of APOA5 and CETP contributed to high-density lipoprotein-cholesterol levels. Variants of CETP and LIPG contributed to non-high-density lipoprotein-cholesterol levels, a finding not reported previously. Sustained hypertriglyceridemia and low high-density lipoprotein-cholesterol during the study period was significantly associated with the genetic score.

CONCLUSIONS

Single nucleotide polymorphisms of ABCA1, APOA5, APOC3, APOE, and CETP contribute to plasma triglyceride and high-density lipoprotein-cholesterol levels during antiretroviral therapy exposure. Genetic profiling may contribute to the identification of patients at risk for antiretroviral therapy-related dyslipidemia.

Risk of cervical cancer associated with Chlamydia trachomatis antibodies by histology, HPV type and HPV cofactors

Human papillomavirus (HPV) is the central etiologic factor for cervical cancer, and prior studies suggested C. trachomatis may act as an HPV cofactor. We examined the C. trachomatis-cervical cancer association by serotype, histology, HPV type in the tumor, and other HPV cofactors. We conducted a population-based study in the Seattle-Puget Sound area of 302 women with invasive squamous cell carcinomas (SCC), 185 women with adenocarcinomas of the cervix (AC), and 318 HPV seropositive control women. The risk of SCC associated with antibodies to C. trachomatis was increased (OR 1.6, 95% CI 1.1-2.2) but not for AC (OR 1.0, 95% CI 0.6-1.5). This association was independent of HPV type in the SCC tumor tissue. There was an association between specific serotypes of C. trachomatis and SCC for 6 of the 10 serotypes: B (OR 3.6, 95% CI 1.5-8.4), D (OR 2.1, 95% CI, 1.2-3.5), E (OR 2.4, 95% CI, 1.4-3.9), G (OR 3.0, 95% CI, 1.1-7.9), I (OR 4.2, 95% CI, 1.5-11.7), and J (OR 2.3, 95% CI, 1.0-5.1), but not for the 4 types (C, F, H, and K) that were present at very low prevalence in this population. There was an increased risk of SCC, but not AC, associated with antibodies to C. trachomatis that was not serotype specific.

Breast cancer risk following radiotherapy for Hodgkin lymphoma: modification by other risk factors

The importance of genetic and other risk factors in the development of breast cancer after radiotherapy (RT) for Hodgkin lymphoma (HL) has not been determined. We analyzed data from a breast cancer case-control study (105 patients, 266 control subjects) conducted among 3 817 survivors of HL diagnosed at age 30 years or younger in 6 population-based cancer registries. Odds ratios (ORs) and excess relative risks (ERRs) were calculated using conditional regression. Women who received RT exposure (> or = 5 Gy radiation dose to the breast) had a 2.7-fold increased breast cancer risk (95% confidence interval (CI) 1.4-5.2), compared with those given less than 5 Gy. RT exposure (> or = 5 Gy) was associated with an OR of 0.8 (95% CI, 0.2-3.4) among women with a first- or second-degree family history of breast or ovarian cancer, and 5.8 (95% CI, 2.1-16.3) among all other women (interaction P = .03). History of a live birth appeared to increase the breast cancer risk associated with RT among women not treated with ovarian-damaging therapies. Breast cancer risk following RT varied little according to other factors. The additional increased relative risk of breast cancer after RT for HL is unlikely to be larger among women with a family history of breast or ovarian cancer than among other women.